Rapid frequency change radio receiver



Oct. 29, 1946. J. F. HUTCHINS ETAL I RAPID FREQUENCY CHANGE RADIORECEIVER Filed Jan. 31, 1944 IAN/EN 'rons MAL/AM A. V J7:

d rioelvgy JIMEs EHUTcH/NJ Patented Oct. 29, 1946 RAPID FREQUENCY CHANGERADIO RECEIVER James F. Hutchins and William K. White, Jr., San Antonio,Tex.

Application January 31, 1944, Serial No. 520,458

(Cl. 250- 20) --(Granted under the act of March 3, 1883, as

4 Claims.

the' invention to provide a her not necessarily predetermined but whichis 'modulated by pulses of a'predetermined pulse rate and apredetermined pulsewidthfi;

A further objectis the provision of a radiolreceivercapable' of openingitself to the reception of transmissions of the above mentioned type tothe exclusion'of other types.

These and other 'ob-jects areattained by the novel circuit: andarrangement of-parts hereinafter described and illustratedv by theaccompanying drawing, forming a parthereof, and in which is shown aschematic diagram'of the circuit employed.

Referring to thedrawing, the receiver is shown to include a conventionalsection comprising a stagel of radio frequency, a first detector 2,three stages, 3, 4, 5, of intermediate frequency, and diodesecond'detector B. 1

Audio signal voltage is .takenat 1 from the second detector 6 in aconventional manner, and is applied to the grid-ofthe first audio tube8. The cathode of tube'8 is not at ground'poten'tial but is connected tothe .plate of an audio blocking tube 9. The cathode of audio blockingtube 9 is at ground potential, and its grid is biased to just belowcut-off so that plate current will flow in tubes 8 and 9 when a positivevoltage is applied to the grid of tube 9.

The portion of the receiver which produces the sweep voltages includes atwin triode tube l0 used as a multi-vibrator to produce a wavesimilar toa sine wave. This multi-vib-rator tube ID will produce waves other thannear sine-waves, but it has been found that a near-sine wave is the typebest suited for this receiver. The frequency sweep voltage produced bymulti-vibrator tube l0 and the associated circuit is impressed across aresistor ll, of approximately one megohm, connected between ground andcathode l2 of a twin triode locking tube l3. The triode includingcathode 12 will be hereinafter designated as triode A, and the othertriode as triode B.

During the negative half-cycle of the sweep voltage impressed across theone megohm reamendedApril 30, 1928;"370 O. G. 757) sistor ll, the plateof triode A assume a like negative potential below ground as there is nocurrent flowing between cathode and plate. The plate of triode A isconnected directly to the grid of tube M, which is simply a voltagephase inverter. A fixed condenser 15 connected to the plate of triode Awill rise and fall in potential in the same manner as the potential ofthe plate or triode A rises and falls.

Its action in so far as causing the receiver .to lock on'a definitefrequency of incoming signal will be hereinafter described.

The outputvolta'ge of inverter tube l4 is oor nectedto the grids of atwin triode tubel 6, which functions. in the same manner as two variableresistances. The conventional part of the receiver employs amulti-vibrator oscillator tube l1 associated with the first detector 2;The frequency'of this multi-vibrator tube l1 can be controlled byvarying the values of the two grid bias resistors connected to the twogrids of the tube. It'is apparent that if these resistances can be madeto vary simultaneously with the varying in frequency of an incomingsignahthe receiver can be made to follow instantaneously any incomingsignalthat jumps from one frequency to another. In order to accomplishthis, the plates and cathodes of tube l6 areconnected, as shown in thediagram, to the multi-vibrator oscillator tube ll in such a way as tocause the plates and cathodes of tub Hi to act in the manner of avariable resistance when connected in parallel with the grid biasresistance of each triode portion of the oscillator tube I1. Varying thecathode to plate resistance of tube US will cause the oscillator tube Hto produce a corresponding change in oscillator signal frequency, andcause the receiver to sweep a band of frequencies. Briefly stated,thereceiver is made to sweep a band of frequencies bythe near-sine waveoutput voltage of the multi-vibrator tube I0 applied to tube l6 throughthe locking tube l3 and phase inverter tube l4, causing a change ingrid-bias resistance in each grid-cathode portion of the oscillator tube11.

As mentioned above, the receiver. among other things, will receive apulsed signal only. The pulse discriminator section of the receiverbegins with the negative automatic volume control taken from the diodedetector 6. This negative voltage is impressed upon the grid of triode Cof a twin-triode discriminator tube 18. The word discriminator has beenchosen as the name of tube 18 as its action causes the receiver todiscriminate between a pulsed and a non-pulsed signal. The positivevoltage pulses produced on 3 the plate of triode C of tube [8 are fed tothe grid [9 of triode D of the tube. This grid I9 is biased sufiicientlybeyond cut-off so that only the peaks of the positive voltage producedby the plate of triode C will allow plate current to flow in the plateof'triode D. It is, therefore, the action of discriminator tube l 8 toallow output plate voltage in triode D only during large peaks producedby the pulsed negative voltage audio signal impressed on the grid oftriode' C. These pulsed voltages are fed from the plate of triode -D oftube IE to the two grids of the locking tube I3, causing plate currentflow to cease in both sections of the locking tube l3, thereby removingthe near-sine wave voltage of the'multi-vibrator' tube l9 from theoscillator tube I1. This causes the oscillator tube ll to stop varyingin frequency, and therefore, causes thezreceiver. to lock on theincoming signal if the voltage producedby the multi-vibrator Hi can bemaintained at the point it had reached at the time the locking tube I 3-was blocked out of. the. circuit. This is accomplished by means ofthefixed condenser l5 whichv is connectedbetween ground and the Dlateoftriode A of tube I 3. Thiscondenser has been-rising and falling in.charge as. the multivibrator near-sine wave voltage has been rising andfalling. inv value, and. has been. discharged by electrons leaking 01T-to ground through triode B of tubel3. The. charge of'the. condenser can.be maintained by blocking this. leak. off path. The leak ofi path isblocked by the output plate volt: ageof;discriminatortube l8 causing thegrid -of triode Bof tube I3Ito. become strongly negative.

The condenser IE is. now' required to maintain its charge, and it willcause the grid'bias of the voltage phaseinvertertube M,- and irrturn thevoltage impressed on tube It, to. be maintained, which fixestheirequency of the oscillator I]; and causes the entire. receiver tolock.on.the incoming signal.

The receiver described abovevvill receive radiationsthat are pulsed andthat vary infrequency. The receiver sweeps a. band of frequencies, andwill open itself up. only. to a. carrier with extremely. high amplitudepulses. This presents twochangesfromthe conventionalitypes of radiocommunication. The first change is in the use of atransmitter thatvaries rapidly in frequency in an unpredeterminedmanner and in.havingareceiverv that will sweep the frequency band in which. the. transmitteris varying and receive thesetransmissions and convert them intointelligible signals. The secondchange is inhaving a transmitter. thattransmits. pulses of predetermined. frequency and having a receiver thatwill discriminate. insuchmanner as to receive these "pulses. only to-theexclusion of other signals.

The invention having been described, what is claimed is:

1'. In a receiver for receiving radio signals which sweep rapidly. overa band of different frequencies, a conventional super-heterodyne radioreceiving circuit havinga first detector and a second detector, amulti-vibrator oscillator connected to the first detector, a secondmulti-vibrator'pro'ducing a, near-sine wave voltage, means controlledbysaid voltage to affect the oscillator to cause the receiver to sweepover a band of frequencies, means associated with the second detector tooperate only upon the reception of pulses of predetermined frequency andamplitude, and means affected by the operation of said last mentionedmeans torender the second multi-vibrator ineffective and lock theoscillator at a definite frequency.

2. A device for converting into intelligible reception a carrier wavesweeping from one frequency to another in an indefinite manner andmodulated by pulses of a predetermined pulse frequency and amplitude,comprising a conventional type of super-heterodyne radio receivercircuit including a, first detector, an oscillator tube connected tosaid first detector, a multivibrator producing a near-sine wave voltage,a triode tube upon which said voltage is impressed, said triodetubebeing connected to the oscillator tube to vary the grid-biasresistance of the oscillator tube to cause the oscillator to follow thewavecf. the multi-vibrator and cause the receiver to sweep over a bandof. frequencies, a discriminator tube connected to said circuit tooperate only upon the reception of. pulses of a predetermined frequencyand amplitude, and means to render the multi-vibrator ineffective andlock the oscillator at a definite frequency when said discriminator tubeis placed in operation.

3. In a device for receiving pulses ofa predetermined repetition rateand amplitude, a radio circuit, an oscillator tube connected to. said.circuit, ,'asecond tube connected to the. oscillator tube andfladaptedto function as a variable resistance, a multi-vibrator producing, avoltage havinga predetermined wave shape, a locking tube connectedto themulti-vibrator, a phase inverter connected to the locking tube andsecond tube to cause the second tube to. act as a variable resistance.and'vary the grid-bias of theoscillator. tube to cause the receivingcircuit to sweep over a band of frequencies,.a discriminator tubeconnectedt'o. the circuit and arrangedto operate only upon the receptionof pulses of a predetermined repetition rate and amplitude, and meansconnecting the locking tube and discriminator tube to discontinue theoperation of thelocking tube and lock" the device at a definitefrequency when the discriminator tube is placedin operation.

4. A device for receivingpulsedradio frequency signals ofpredeterminedrepetition rate, and amplitude which sweep rapidly over aband of different carrier frequencies, comprisingasuperheterodynereceiver including a first detector, an oscillatorconnected to said first detector, means including a. second oscillatorto vary said first oscillator to cause the. receiver to sweep over aband of carrier frequencies, means to cause said receiver to becomeoperative to produce a signal output only upon the reception of pulses.of a predeterminedv repetition rate. and amplitude, and meansconditioned by said last mentioned means to render said secondoscillator ineifective and to lock said first oscillator at a definitecarrier frequency.

JAMES F. HUTCHINS.

WILLIAM K. WHITE, JR

